1. Field of the Invention
The present invention relates to magnetic recording and reproduction apparatuses and methods therefor, and more particularly, to a magnetic recording and reproduction apparatus and a method therefor, in which digital data is recorded by a helical scanning method or reproduced.
2. Description of the Related Art
Portable digital video tape recorders including cameras (digital camcorders) and installation-type digital video tape recorders have been available these days, which record digital video signals and digital audio signals into magnetic tape.
As a recording method for the above digital video tape recorders, a so-called DV method (IEC 61834 Helical scan digital video tape cassette recording system using 6.35 mm magnetic tape for consumersxe2x80x94525/60, 625/50, 1125/60, and 1250/50 systems) is used. The assignee of the present invention has filed two related applications (U.S. Pat. No. 5,926,604 and No. 6,028,726).
In the DV method, video tape 6.35 mm (=xc2xc inches) wide is used, which is narrower than video tape used in related analog video tape recorders by their recording methods, such as a so-called 8-mm method (IEC 60843 Helical scan video tape cassette recording system using 8 mm magnetic tape for consumers).
In the DV method, although the tape width is smaller than that conventionally used, since a signal to be recorded is compressed and a recording density is increased, the DV method allows higher-quality recording for a longer period than recording methods for related analog video tape recorders.
A track structure in the DV method is as follows: from the top of a track, an insert-and-track-information (ITI) sector serving as a time-axis reference during so-called after recording, an interference area (ITG: Inter track gap) (GAP1), an audio (Audio) sector, another interference area (GAP2), a video (Video) sector, yet another interference area (GAP3), and a sub-code (Sub-code) sector are sequentially disposed.
In the DV method, the ITI (ITI) sector is provided for a track in order to use data recorded in the ITI (ITI) sector as a positional reference in the rotating direction (time-axis direction) of the rotating drum so that time-axis information required for after recording of audio and video into a track on the tape can be obtained from the timing when the data recorded in the ITI sector is read.
Data recorded in the ITI (ITI) sector is not rewritten even if a part of data recorded in a track is rewritten, for example, in after recording of video and audio. The data in the ITI (ITI) sector is used for tracking servo during after recording. Therefore, the level of a pilot signal for servo is enhanced (the signal level is increased) in the ITI (ITI) sector as compared with in the other portion of a track.
There is a method (hereinafter called a digital 8-mm method) in which digital data of two tracks in the above DV method is continuously recorded in one track on magnetic tape (8 mm wide) wider than that used in the DV method. Also in this digital 8-mm method, the ITI (ITI) sector is used for the same purpose so as to maintain compatibility with the DV method in terms of circuits such as an LSI.
A positional shift at starting points between two adjacent tracks on magnetic tape is generally called a sync lag (Sync-lag). Sync lags in the DV method and the digital 8-mm method are 6.1 xcexcs and 20.3 xcexcs, respectively, and the sync lag in the digital 8-mm method is about three times that in the DV method. This is due to a geometrical difference in track pattern between the DV method, which uses a track pitch of 10 xcexcm and a track recording angle of about 10 degrees, and the digital 8-mm method, which uses a track pitch of 16.34 xcexcm and a track recording angle of about 5 degrees.
Since data recorded in the ITI (ITI) sector is read when a head is on the track, there is no problem to use the data as a positional reference in the rotation direction of a rotating drum. During after recording, a sync lag causes some effect when a pilot signal is read from an adjacent track for achieving tracking servo.
As shown in FIG. 6 and FIG. 7, which show track conditions near ITI (ITI) sectors in the digital 8-mm method and the DV method, respectively, it is understood that a period of time when a magnetic head can read pilot signals on upper and lower tracks at the same time is very short (4.59xe2x88x922xc3x976.1=33.7 xcexcs for the DV method whereas 45.9xe2x88x922xc3x9720.3=5.3 xcexcs for the digital 8-mm method). It is very difficult to obtain correct information for achieving tracking servo within as short as 5.3 xcexcs in the digital 8-mm method, depending on the time constant of a filter for the pilot signal and an error in sampling time.
Accordingly, it is an object of the present invention to allow data recorded in the ITI sector, which serves as a time-axis reference during after recording, to be correctly read to obtain correct information for achieving tracking servo.
The foregoing object is achieved in one aspect of the present invention through the provision of a recording and reproduction method for recording digital data on magnetic tape by a helical scanning method or for reproducing digital data recorded on magnetic tape by the helical scanning method, including the steps of generating a plurality of sectors in each track on the magnetic tape and recording various types of data, such as video data and audio data, and track-synchronization data; recording pilot signals for tracking control on the various types of data in a superposition manner by the use of three different frequencies such that the frequency changes every track in a predetermined repetition manner; and recording the pilot signal so as to have a higher level at least in two blocks in a sector where the track-synchronization data is recorded than in the other portion of each track.
Since the level of the pilot signal has been increased at many portions, pilot signals recorded in adjacent tracks can be detected at the same time within an extended period of time during after recording. Data recorded in the ITI sector, which serves as a time-axis reference, is therefore correctly read and tracking servo is successfully applied.
The foregoing object is achieved in another aspect of the present invention through the provision of a recording and reproduction apparatus for recording digital data by a magnetic head on magnetic tape by a helical scanning method or for reproducing by a magnetic head digital data recorded on magnetic tape by the helical scanning method, including a circuit for generating a plurality of sectors in each track on the magnetic tape and for recording various types of data, such as video data and audio data, and track-synchronization data; a circuit for recording pilot signals for tracking control on the various types of data in a superposition manner by the use of three different frequencies such that the frequency changes every track in a predetermined repetition manner; and a circuit for recording the pilot signal so as to have a higher level at least in two blocks in a sector where the track-synchronization data is recorded than in the other portion of each track.
Since the level of the pilot signal has been increased at many portions, pilot signals recorded in adjacent tracks can be detected at the same time within an extended period of time during after recording. Data recorded in the ITI sector, which serves as a time-axis reference, is therefore correctly read and tracking servo is successfully applied.
The level of a pilot signal in all blocks in the track-synchronization-information sector may be made higher than that in the other portion of each track. In this case, since the levels of pilot signals have been increased at more portions, pilot signals recorded in adjacent tracks can be detected at the same time in a further extended period of time during after recording. Data recorded into the ITI sector, which serves as a time-axis reference, is correctly read, and therefore, it becomes extremely easy to apply tracking servo.
Data may be recorded in each track by the additional use of a flying erase head. In this case, previous data does not remain. An adverse effect of remaining data does not occur.